One example of a conventional air conditioner is the air conditioners used to condition the air of office buildings. This kind of air conditioner includes chiefly a heat source unit having a compressor and a heat-source-side heat exchanger, a user unit having a user-side heat exchanger, and gaseous refrigerant piping and liquid refrigerant piping for connecting said units together. In view of such environmental concerns as destruction of the ozone layer, HFC (hydrofluorocarbon) refrigerants have come to be used as the working refrigerant in such air conditioners.
When air conditioners in existing buildings are updated or replaced, the existing gaseous refrigerant piping and liquid refrigerant piping is sometimes reused as is in order to reduce the cost and time required for the replacement work. In such cases, the air conditioner installation work proceeds chiefly according to the following steps:
<1> Recover refrigerant
<2> Install equipment
<3> Install piping and wiring (reuse existing gaseous refrigerant piping and liquid refrigerant piping)
<4> Pull vacuuming
<5> Charge system with refrigerant
With this work procedure, the work time can be reduced chiefly by simplifying the piping and wiring work.
However, debris, oil, and other residual contaminants that remain in existing gaseous refrigerant pipes and liquid refrigerant pipes must be removed by cleaning the piping before running the air conditioner in the normal fashion. More particularly, if the existing air conditioner used a CFC (chlorofluorocarbon) or HCFC (hydro-chlorofluorocarbon) refrigerant as the working refrigerant, old refrigerant oil for the CFC (chlorofluorocarbon) or HCFC (hydro-chlorofluorocarbon) refrigerant will remain in the existing gaseous refrigerant piping and liquid refrigerant piping. Consequently, the old refrigerant oil will not be compatible with the new refrigerant oil for the HFC refrigerant and will behave as a contaminant in the refrigerant circuit, possibly clogging expansion valves and capillaries in the refrigerant circuit and damaging the compressor.
The refrigerant oils used for the conventional CFC and HCFC refrigerants are naphthene-based mineral oils and other non-polar oils. Conversely, the oils used for the newer HFC and HC refrigerants are ester-based and ether-based mineral oils and other polar oils. Consequently, if refrigerant oil for a CFC or HCFC refrigerant remains in the piping, the solubility of the refrigerant oil in the working refrigerant will change and the proper refrigeration performance will not be obtained from the HFC refrigerant. Thus, it is also necessary to clean the refrigerant piping in view of this issue of refrigerant oil compatibility.
Several refrigerant pipe washing methods have been proposed that enable existing gaseous refrigerant piping and liquid refrigerant piping to be reused when an air conditioner is updated or replaced.
One such method uses an HCFC refrigerant (e.g., HCFC141b and HCFC225) in which mineral-oil-based refrigerant oils have a high solubility as a cleaning agent.
A second method uses repeated batch washing with an HFC refrigerant after the heat source unit and user unit have been replaced (Japanese Patent Registration No. 3149640).
A third method involves providing an oil collecting device in the refrigerant circuit in addition to updating the heat source unit and user unit and washing the existing refrigerant piping by operating the air conditioner in a mode that circulates the new HFC refrigerant (Japanese Patent Registration No. 3361765 and Japanese Laid-Open Patent Publication No. 2001-41613).
The first refrigerant pipe washing method washes in a highly effective manner because it uses an HCFC refrigerant in which the mineral-oil-based residual refrigerant oil has a high solubility, but it should not be used in view of such environmental concerns as destruction of the ozone layer.
The second refrigerant pipe washing method is environmentally friendly because it uses an HFC refrigerant, but the requirement of repeated batch washings consumes a large quantity of refrigerant and makes the method uneconomical.
The third refrigerant pipe washing method eliminates the need for repeated batch washings because it enables continuous washing with an operating mode that circulates the refrigerant. Thus, the method is economical in that it can reduce the amount of refrigerant used.
However, if the new heat source unit and user unit use R407C or R134a as the working refrigerant, the third refrigerant pipe washing method will not be very effective at cleaning the refrigerant pipes because mineral-oil-based refrigerant oils have a low solubility in R407C and R134a. Consequently, the quantity of refrigerant circulated and the time spent in the pipe washing mode will both tend to increase. This issue also applies to the second refrigerant pipe washing method in that the number of batch washings and the amount of refrigerant used in each batch increases due to the poor solubility.